XT350 lightweight adv

OBS460

Well-known member
I put 115 miles on the XT today and logged oil temps.

65mph+ is now 30F+ cooler (used to run 245-255F, now it stabilizes around 215F), about 20F cooler around town (used to sit at 230F in stop and go, now it's around 205-210F). It cools off much faster once moving from a stop, before once heat soaked it didn't want to cool down at all.

All in all I'd call it a win! For $45, I can't complain about these findings at all. It should help extend oil life, so I can change it less and recuperate my money spent.
 

OBS460

Well-known member
I've noticed that the XT consumes a little oil when ran above 5000rpms for a period of time (commuting to work). The compression tests out strongly, there's no oil deposits on the plug, and no smoke indicating excessive blow by. There was also a slight amount of weeping out of the valve cover gasket (new gasket).

Looking at the factory breather arrangement, I noticed it was a simple hose leading to the air box. The issue is with a single cylinder engine, the piston is moving the same amount of air in the combustion chamber as it is in the lower end. Without some sort of check valve, you end up with a large amount of air cycling back and forth.

As a cheap experiment, I added a brake booster check valve in line to the air box. I then ran the engine at 5000rpms with the breather disconnected, and again connected with the valve.

20210914_104135.jpg

With an open hole, the crankcase built slight positive pressure.

20210914_134129_exported_98309.jpg

Reconnecting the tube with the check valve brought it down to a net zero pressure. This should promote better ring seal, as well as minimize air movement (and oil escaping as a byproduct).

20210914_134206_exported_122470.jpg

When I got to work today I didn't notice any weeping from the valve cover, so it appears to be promoting better drainage to the lower end. I may expirement more with adding a breather on the clutch side as well and see if I can get it to draw a vacuum overall and add a little performance.
 

calicamper

Expedition Leader
I've noticed that the XT consumes a little oil when ran above 5000rpms for a period of time (commuting to work). The compression tests out strongly, there's no oil deposits on the plug, and no smoke indicating excessive blow by. There was also a slight amount of weeping out of the valve cover gasket (new gasket).

Looking at the factory breather arrangement, I noticed it was a simple hose leading to the air box. The issue is with a single cylinder engine, the piston is moving the same amount of air in the combustion chamber as it is in the lower end. Without some sort of check valve, you end up with a large amount of air cycling back and forth.

As a cheap experiment, I added a brake booster check valve in line to the air box. I then ran the engine at 5000rpms with the breather disconnected, and again connected with the valve.

View attachment 682097

With an open hole, the crankcase built slight positive pressure.

View attachment 682098

Reconnecting the tube with the check valve brought it down to a net zero pressure. This should promote better ring seal, as well as minimize air movement (and oil escaping as a byproduct).

View attachment 682099

When I got to work today I didn't notice any weeping from the valve cover, so it appears to be promoting better drainage to the lower end. I may expirement more with adding a breather on the clutch side as well and see if I can get it to draw a vacuum overall and add a little performance.
Interesting testing. Thanks for sharing
 
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